1. Technical Field
The present invention relates to a liquid ejecting head which ejects liquid droplets from a nozzle by displacement of a piezoelectric element, and a liquid ejecting apparatus.
2. Related Art
As an ink jet recording head which is a representative example of liquid ejecting heads which eject liquid droplets, for example, there is an ink jet recording head, which is provided with a flow path forming substrate forming a pressure generation chamber, and a piezoelectric element configured by a lower electrode disposed on one surface side of the flow path forming substrate, a piezoelectric layer disposed on the lower electrode, and an upper electrode disposed on the piezoelectric layer, and which ejects ink droplets from a nozzle by displacing a vibrating substrate by displacement of the piezoelectric element so as to apply pressure in the pressure generating chamber. In such a configuration of an ink jet recording head, when displacing a vibrating substrate by driving of the piezoelectric element, there is a problem that it is easy for cracks to be generated in a section of the vibrating substrate opposing an edge portion in the longitudinal direction of the pressure generating chamber.
In order to solve this problem, a piezoelectric element is provided with a piezoelectric active section which is a driving section in practice and a piezoelectric nonactive section which has a piezoelectric layer connected to the piezoelectric active section but is not driven in practice (for example, refer to Japanese patent No. 3114808).
By providing such a piezoelectric element with a piezoelectric nonactive section, when the piezoelectric element is driven, the amount of deforming of the vibrating substrate opposing the edge portion in the longitudinal direction of the pressure generating chamber is reduced and the generation of cracks in the vibrating substrate can be suppressed.
Here, the piezoelectric element is one configured by a first electrode (the lower electrode) which is an individual electrode disposed on the flow path forming substrate, a piezoelectric layer, and a second electrode (the upper electrode) which is a common electrode. Even in the case of a piezoelectric element with this configuration, the generation of cracks in the vibrating substrate can be suppressed by providing a piezoelectric active section and a piezoelectric nonactive section described above.
Furthermore, in the piezoelectric element where the second electrode is the common electrode, the piezoelectric nonactive section is formed by, for example, removing the second electrode. That is, the boundary of the piezoelectric active section and the piezoelectric nonactive section is defined by the edge portion of the second electrode. Even with this piezoelectric element, cracks in the vibrating substrate can be suppressed as described above by providing the piezoelectric nonactive section.
However, if the second electrode does not exist on the piezoelectric nonactive section, stress is concentrated in the boundary portion of the piezoelectric active section and the piezoelectric nonactive section, and there is a concern that cracks may be generated in this portion of the vibrating substrate. Explaining in further detail, since the second electrode which configures the piezoelectric element is, for example, formed of iridium or the like and has internal stress in a compression direction, in an initial state (a state where a voltage is not applied), the piezoelectric active section is pulled in practice in an opposite direction to the pressure generating chamber by the second electrode, and the second electrode side is bent and deformed to be convex in a cross section in a width direction (lateral direction) of the pressure generating chamber. On the other hand, in the piezoelectric nonactive section which is not provided with the second electrode, the first electrode side is bent and deformed to be convex, which is opposite to the piezoelectric active section. As a result, stress is concentrated in the boundary portion of the piezoelectric active section and the piezoelectric nonactive section, and there is a concern that cracks may be generated in that portion of the vibrating substrate.
It is particularly easy for this problem to occur in cases where the second electrode is the common electrode of the piezoelectric element. This is because if the second electrode is the common electrode of the piezoelectric element, since the area of the second electrode which configures the piezoelectric element (piezoelectric active section) becomes comparatively large, there is a large amount of bending of the piezoelectric active section in the initial state, compared to a case where the second electrode is the individual electrode.